In the case of an incompletely filled fuel tank, the problem fundamentally exists that at a corresponding temperature and a corresponding pressure, an ignitable mixture of fuel gases and oxygen in air can form in the tank at an interface between the surface of the liquid fuel held in the tank and a layer of air lying above. This mixture may be ignited by a spark, which may for example be due to an electrical short circuit or the like, and cause an explosion of the fuel tank. Particularly when the fuel tank is a kerosene tank of an aircraft, such a tank explosion may have catastrophic consequences and sometimes even lead to loss of the aircraft.
Particularly for fuel tanks on board an aircraft, attempts are therefore made to counteract the risk of a tank explosion by delivering an oxygen-free or at least low-oxygen and therefore inert protective gas to an incompletely filled fuel tank, so as to prevent the formation of an ignitable mixture of fuel gases and oxygen in air. For example, nitrogen may be used as the protective gas. The protective gas to be delivered to the fuel tank, however, must be either placed in a separate storage container on board the aircraft or obtained in a comparatively elaborate way, for example by using a molecular sieve to separate nitrogen from air.
DE 100 31 238 B4 discloses a fuel cell system which comprises a gas generating system box, for example containing components of a reforming system, a peripherals box containing peripheral components, a fuel cell box and a process media supply box containing compressors and densifiers for delivering process air. In order to avoid accumulation of leakage hydrogen in the boxes of the fuel cell system, the boxes of the fuel cell system are flushed. Ambient air or exhaust gas from the fuel cell system may be used as the flushing medium.
DE 102 40 379 A1 and DE 198 45 955 A1, respectively, disclose systems for inerting aircraft tanks, in which correspondingly processed combustion exhaust gases of a turbine engine are delivered to the tanks.
JP 2005100846 A relates to a fuel cell system in which cycled exhaust gases of an oxygen electrode are delivered to a hydrogen electrode.
DE 103 56 012 A1 and DE 102 49 588 A1, respectively, disclose a fuel cell system employed on board an aircraft, which is used to generate water and energy on board the aircraft.
Lastly, the use of a PEM fuel cell on board an aircraft to substitute for a main power unit generator, an auxiliary power unit, a ram air turbine or a NiCd battery, is known from DE 198 21 952 C2.